Hexafluoroisopropanol (1,1,1,3,3,3-hexafluoro-2-propanol, abbreviated herein as HFIP) is used as an intermediate for pharmaceuticals and agrochemicals, as a solvent or cleaner in electronics, and in analytical applications due to its ability to dissolve a variety of polymers. HFIP exhibits strong hydrogen bonding and will associate with and dissolve most molecules with receptive sites such as oxygen, double bonds, or amine groups. Stable distillable complexes are formed with many ethers and amines due to strong hydrogen bonding. HFIP is soluble in water and most organic solvents. It is a volatile (b.p. 58.2° C.) and polar material, with high density, low viscosity, and low surface tension. HFIP is transparent to UV light and has a low refractive index.
Typically, hexafluoroisopropanol (HFIP) is prepared by the hydrogenation of hexafluoroacetone (HFA) and/or HFA hydrate, for instance using a batch reactor containing a slurry catalyst. Such processes have limited capacity and relatively long cycle times; while catalyst attrition, removal of catalyst fines, and catalyst recovery are problematic.
Katsuhara et al. in U.S. Pat. No. 4,564,716 describe a process for the hydrogenation of HFA hydrate using a heterogeneous catalyst system that is typical of batch hydrogenation processes. Katsuhara et al. disclose HFA hydrate is hydrogenated rather than HFA, to reduce concerns with reacting high concentrations of toxic HFA and the pressures that would be required to contain the low boiling HFA (−28° C.) at reaction temperatures (700-100° C.). In this process the catalyst settles in the reactor at the end of a batch. A portion of the liquid product is then drawn off, but about 10% of the catalyst is drawn off with the liquid, requiring added catalyst to make-up the initial charge, and complicating catalyst recovery.
Batch hydrogenation has deficiencies compared with continuous processes, for instance the energy and cycle time that are required to heat up and cool down each batch. As a result, the reaction time in a batch process is only a fraction of the overall cycle time, and therefore the productivity of the reactor is much lower than for a continuous system.
Kawai et al., in GB 2,073,181, describe a process for the continuous vapor phase hydrogenation of HFA to form HFIP by passing a mixture of HFA and hydrogen across a fixed bed of solid catalyst at 300-140° C. While an improvement over a batch process, vapor phase hydrogenation processes also have disadvantages. There is a high temperature rise across the catalyst bed due to the heat released from the exothermic hydrogenation reaction. This temperature rise can cause catalyst bed hot spots, which can result in byproduct formation, including the formation of hydrofluoric acid, and reduced catalyst life.
Demand for HFIP in the applications listed above is increasing rapidly. It is desirable to improve available processes for the hydrogenation of HFA. The present invention provides such a process.